Without limiting the scope of the present invention, its background will be described in relation to activating perforating guns, as an example.
One of the typical steps in completing a well that traverses a hydrocarbon bearing subterranean formation is perforating the well casing to allow production of a hydrocarbon fluid such as oil or gas. In some wells, the hydrocarbon bearing subterranean formation is continuous, which allows the casing adjacent to the formation to be perforated in a single trip into the well with one or more guns that create openings along the entire productive zone. In other wells, however, it has been found that the productive zones of a formation are not continuous. For example, some formations may have non-productive streaks in the oil-bearing zone. In other cases, the well may traverse multiple formations that are separated by non productive intervals. In well having such multiple zones or multiple formations, it remains desirable to perforate the individual zones or formations at separate well depths during a single trip into a well.
Attempts have been made to perforate such multiple zones in a single trip using multi-gun strings and selective fired gun systems. Typically, the guns in such a multi-gun string are sequentially armed and fired starting from the lowermost gun and progressing to the uppermost gun using a variety of mechanical and electrical techniques. For example, in certain gun systems, each gun above the lowermost gun is sequentially activated responsive to the force of a detonation of the gun below. In such gun systems, mechanical switches are used to step through the guns from the bottom to the top. It has been found, however, that these selective fired gun systems encounter a number of problems. For example, certain guns in these selective fired gun systems may fail to fire because of assembly mistakes, mechanical integrity issues, switch failures and the like. In addition, it has been found, that guns may become prematurely armed due, for example, to electrical or mechanical failures which may lead to off depth firing of the misarmed gun. Also, in some systems, if any gun fails to fire for any reason, the gun above will not be armed and the firing sequence is stopped. As a result, the guns must be pulled out of the well for repair or replacement.
More recently, attempts have been made to improve selective fired gun systems by allowing downhole control units to be individually addressed by a surface system. In such systems, a request and response protocol has been used to allow communication between the surface system and the downhole control units such that the identity of the downhole control units may be confirmed prior to activating a gun. It has been found, however, that such individually addressable selective fired gun systems require each of the downhole control units to communicate over a long distance to the surface system. In addition, it has also been found, that such individually addressable selective fired gun systems fail to provide any information regarding the quality of the perforating results. For example, certain failures in firing, including low order firing, may go undetected with such systems resulting in non productive or under productive completions.